1. Field of the Invention
The present invention relates to a common mode choke coil for removing common mode noises which are superimposed in a power supply line, a signal line or the like of an electronic equipment. The present invention also relates to a method of manufacturing the common mode choke coil.
2. Description of the Related Art
The following common mode choke coil and a method of manufacturing the same are known from Japanese Published Unexamined Patent Application No. 304035/1993. Namely, inside a resin which is mixed with powder of a magnetic material, two metallic coils which have the same number of winding and the same winding direction are buried substantially in parallel to each other in a substantially coaxial manner, whereby a formed body made of a resin mixed with powder of magnetic material is obtained. An electrode which is electrically connected to a corresponding end portion of each of the metallic coils is thereafter formed.
In the above-described conventional common mode choke coil, two metallic coils are separately or independently formed and are buried into the resin which has mixed therein powder of the magnetic material. In the process of manufacturing it, the two metallic coils shall not come into contact with each other. Therefore, the powder of the magnetic material will inevitably have to be interposed between the two metallic coils. As a result, an independent magnetic path for each of the metallic coils will be formed through the magnetic material interposed between both the coils. An independent magnetic path thus formed for each of the coils will generate an impedance not only to the common mode noises but also to the normal mode noises. As a consequence, if the common mode choke coil is connected to a signal line, the impedance works as a load to the signal, resulting in an abnormality in the signal wave form.
On the other hand, if two electrically insulating coated conducting wires are wound around a core which is made up of a bar-shaped or drum-shaped magnetic material, it is possible to prevent the magnetic material from being interposed between both the conducting wires. However, this arrangement is not preferable as a common mode choke coil because the frequency characteristics become high in Q value if the conducting wires are not covered on their outside with a sintered magnetic material.
In view of the above-described problems associated with the conventional common mode choke coil and a method of manufacturing the same, the present invention has an object of providing a common mode choke coil whose Q value is not high and whose impedance to the normal mode noises is low, as well as providing a method of manufacturing the same.